Fertility, Human

BIBLIOGRAPHY

The term fertility refers to the actual production of children. It may be distinguished from fecundity, which is the capability to produce children. Demographers make this important distinction, but not all scientists do. Medical scientists, for instance, use the term fertility to refer to reproductive ability. Also, the meaning of the terms of fertility and fecundity are reversed among French-speaking and Spanish-speaking demographers. They too distinguish between the potential and actual production of children. But French-speaking demographers use the term fertilité, and Spanish-speaking demographers the term fertilidad, to refer to reproductive ability, and fecundité and fecundidad, respectively, to refer to actual reproductive performance.

One of the most popular and easily understood and interpreted methods for quantifying fertility is the crude birth rate (CBR), that is, the number of births in a population in a given year, per one thousand members of the population, expressed as follows:

Using 2005 data for China (Population Reference Bureau 2005), the equation becomes:

This means that in China in 2005, there were twelve babies born for every thousand persons in the population. Crude birth rates among the countries of the world in 2005 ranged from lows of nine in several countries, including Japan, Germany, Bulgaria, Poland, Italy, Hungary, and Greece, to highs of fifty-six in Niger and fifty in Liberia, Mali, Malawi, and Guinea-Bissau (Population Reference Bureau 2005). The range of crude birth rates is much greater than that for crude death rates, which in 2005 extended from a low of one in the United Arab Emirates to a high of twenty-eight in Botswana and Lesotho.

Lay persons employ the CBR more often than any other fertility measure, but it is not the most accurate of the measures. The CBR’s denominator does not truly represent the population for which the possibility of giving birth is an issue because it includes males, prepuberty females, and postmenopausal females. Demographers refer to the population in the denominator as the “risk population.” Because of this overly inclusive denominator, the CBR should be interpreted with caution.

Demographers use more refined fertility measures, including the general fertility rate (GFR), age-specific fertility rates (ASFR), the total fertility rate (TFR), the gross reproduction rate (GRR), and the net reproduction rate (NRR). The GFR, ASFR, and TFR are increasingly more accurate measures of the childbearing experiences of a population. The GRR and the NRR measure not fertility but reproduction, that is, the production of females (Rowland 2003).

Fecundity can be divided into five categories on the basis of the extent of fecundity impairment and the degree of certainty regarding this impairment. Badenhorst and Higgins (1962, p. 281) note that all couples may be classified as either fecund or sub-fecund ; the latter may be subdivided into the following groups: definitely sterile, probably sterile, semi-fecund, and fecundity indeterminate. Badenhorst and Higgins define the sub-fecund groups as follows: definitely sterile couples are those “for whom conception is impossible because of certain physical or medical conditions, including an operation or other physical impairment or menopause”; probably sterile couples are those “for whom a birth is improbable on the basis of specific medical evidence”; semi-fecund couples are those who have married or cohabited for a relatively long time without using contraception but have not conceived; fecundity indeterminate couples are those who meet the criteria for semi-fecund couples, “except that the wife sometimes reported douching ‘for cleanness only’ soon after intercourse” (that is, a form of contraception is used). These couples are defined as fecundity indeterminate because they could be potentially fecund and some of them are observed to be fecund as well (Badenhorst and Higgins 1962). Demographic research has shown that the majority of sub-fecund couples are impaired according to one of the above definitions.

As for fertility, demographers have conducted extensive studies examining its trends and determinants. It has been found that during the past few decades, fertility in most countries of the world is in a declining pattern, and this is particularly the case in the more industrialized countries. Beginning in the 1990s, fertility below the replacement level of 2.1 children per woman (as measured using the total fertility rate) has emerged in many countries of the world (Kohler et al. 2002, Morgan 2003). Among the 205 countries worldwide (a country is defined here as a territory with at least 150,000 population), 73 had fertility rates at or below the replacement level in 2005. Following Billari (2004), we refer to fertility as being “low” when the TFR is below the replacement level of 2.1, as being “very low” when it is below 1.5, and as being “lowest low” when it is below 1.3. In 2005, eleven countries reported “lowest low” fertility, that is, a fertility rate below 1.3; these countries include South Korea, Taiwan, Poland, the Czech Republic, Slovakia, and Ukraine.

A number of theories have been proposed to explain the dynamics of fertility. Prominent explanations include proximate determinants theory (Bongaarts, 1994), demographic transition theory (Notestein 1945, Thompson 1929, Davis 1963, Hirschman 1994, Knodel and van de Walle 1979, Poston 2000), wealth flows theory (Caldwell 1976), human ecological theory (Browning and Poston 1980, Kasarda 1971, Poston and Frisbie 2005, London 1987, London and Hadden 1989), political economic theory (Greenhalgh 1990, Kertzer and Hogan 1989), and diffusion theory (Coale and Watkins 1986). Many of these theories use proximate determinants of fertility (proportion married, contraception use, induced abortion, and duration of fertility period) and other social, economic, ecological, political, and cultural factors to understand the dynamics of fertility change.

One limitation of the above fertility measures and theories is that they are usually derived from calculations and analyses only of females. The fertility of men and the determinants of male fertility are rarely examined and compared with those of females. Males are a neglected minority in fertility studies. Several reasons have been proposed to justify this exclusion. Some biological reasons are that the fecundity, and the childbearing years of women occur in a more sharply defined and narrower range (fifteen to forty-nine) than they do for men (fifteen to seventy-nine). In addition, “both the spacing and number of children are less subject to variation among women; a woman can have children only at intervals of 1 or 2 years, whereas a man can have hundreds” (Keyfitz 1977, p. 114). Some methodological justifications are that data on parental age at the birth of a child are more frequently collected on birth registration certificates for the mothers than for the fathers. When such data are obtained for mothers and fathers, there are a greater number of instances of unreported age data for fathers, and this is especially the situation for births occurring outside marriage. The sociological reasons include the fact that men have been regarded principally as breadwinners and “as typically uninvolved in fertility except to impregnate women and to stand in the way of their contraceptive use” (Greene and Biddlecom 2000, p. 83).

However, biological and demographic studies provide evidence that men are important to fertility outcomes and related behaviors. Considering mammalian species in general, Coleman indicates that “the male sex as a whole contributes an equivalent amount of genetic information to the next generation as the female, but the variance contributed by that of males to the next generation in many species—especially those which practice polygamy—is considerably greater than that of the female sex” (p. 33). That is, most females reproduce, some males do not reproduce, and other males have a large amount of offspring. In addition, biologists have found there are more childless males than childless females in many species (Coleman 2000).

Demographically, it has been shown that men have different patterns of fertility and fertility-related behavior. For men, age-specific fertility tends to start later, stops much later, and remains higher than that of women (Paget and Timaeus 1994). The total fertility rates (TFRs) for males and females also differ. Results show that in most industrialized countries male TFRs were historically higher than female TFRs. Over time this gap narrowed and eventually a crossover occurred between these rates. This means that men and women who conformed to the sex- and age-specific fertility rates of an area at one point in time and had less than 2.2 children during their child-bearing years were more likely to have similar than dissimilar fertility (Zhang 2007; Coleman 2000; also see Smith 1992, and Myers 1941).

The special importance of men is also seen in determinants of fertility and fertility-related behaviors such as cohabitation, marriage, and employment. Whereas the focus has been on women’s fertility, in the United States it is men’s fertility that is more likely to be influenced by marital and employment status. Being ever married and ever working significantly increases men’s number of children ever born (CEB), whereas such factors do not have as strong of an impact on women, despite the frequent emphasis on the relevance of labor force participation for women’s fertility (Zhang 2007). Research using various independent variables from several fertility paradigms— namely, human ecology, political economy, and wealth flows—to predict both male and female TFRs for the counties of Taiwan has shown that the variables have consistently performed better in predicting variation in female TFRs than in male TFRs (Zhang 2007).

Men also have different cohabitation and marriage patterns from women. In the United States, for birth cohorts born between 1958 and 1987, it has been shown that living alone, being foreign-born, and living in fragmented families increase the odds of cohabitation for women but not for men. Foreign-born men are more likely to marry than native-born men. But these factors do not have as significant an impact on women’s marriage behavior. In Europe, researchers have conducted studies examining male and female transitions to adulthood in twenty-four countries using survey data for the 1980s and 1990s. They find that educational attainment’s generally negative effect on fertility is stronger for women than for men. Also, unemployment leads to men’s postponement of marriage, whereas it affects women in two distinct ways. It either accelerates or slows down women’s timing of marriage. The effect of religion is stronger among women than men. Furthermore, being Catholic and attending church services affect men and women’s parenthood timing in different ways in predominantly Catholic countries. Other relevant factors such as parental influence have been shown to have a different impact for males compared to females (Corijn and Klijzing 2001).

Historically, women have been tied to motherhood, and this association is deeply rooted in law and policy, in the ways that jobs are structured, and the ways that family relations are navigated. Many of the studies of fertility and parenthood undertaken by demographers have been shaped by this historical association as well (Riley 2005). Together with the biological and methodological factors stated above, this has resulted in the decreased attention given to males in fertility research. Yet, as mentioned earlier, biological and demographic analyses have shown that fertility and parenting are not simply female issues—they are issues involving both men and women. The study of fertility should not only focus on females. Critical demography has promoted bringing men into population studies (Horton 1999; Coleman 2000) and Greenhalgh (1990) and others have argued that it is necessary to incorporate gender studies into studies of demography in order to gain a more balanced picture of demographic issues. Together with lowest-low fertility, unbalanced sex ratios at birth, and the demography of gay males and lesbians, male fertility and men’s influence on decisions about bearing and rearing children have become emerging issues of population study.

SEE ALSO Demography; Gender; Population Growth

BIBLIOGRAPHY

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Zhang, Li. 2007. Bringing Men In: Analyses of Male and Female Fertility. Unpublished PhD diss., Texas A&M University.

Dudley L. Poston Jr.

Li Zhang

Heather K. M. Terrell